In secondary metallurgy metallurgical vessels are used that have in their base a gas flushing brick which in general is replaceable and through which an inert gas, for example argon, is blown into the melt to be treated. Such flushing bricks may be made of a porous shaped brick and the flushing gas may issue through their front face in finely divided form, or they may have gas passages through which the flushing gas enters the melt at the front face of the flushing brick or shaped brick. In addition, so-called joint or gap flushers are known in which a shaped brick of refractory material is surrounded by a sheet metal jacket and the flushing gas passes out peripherally between the shaped brick and the sheet metal jacket and enters the melt.
Such a joint flusher having a shaped brick of refractory material is known from German Offenlegungsschrift 36 06 322, and consists of a base plate having a central gas supply pipe connected to a conical sheet metal jacket. In the jacket there is a shaped brick surrounded by a gas-permeable layer of cement. The shaped brick rests on spacers so that beneath it a gas distribution chamber is formed which is connected to and has the same area as the gas supply pipe through which the flushing gas enters the cement layer.
Since the gas distributing chamber extends as far as the gas-tight metal jacket, the shaped brick is subjected over its whole bottom surface to the extraordinarily high pressure of the flushing gas. Furthermore in the case of such flushing bricks the different coefficients of expansion of the sheet metal jacket and the refractory material of the brick can result in expansion cracks and to the formation of additional gaps through which flushing gas issues uncontrolled. At the places where the gas issues there is then as a rule accelerated wear of the shaped brick, leading to early failure of the flushing brick. Reduction is the size of the bottom surface to reduce the pressure loading on the shaped brick is mostly not possible, since this also reduces the taper of the flushing brick. This gives rise to difficulties in replacing the flushing brick, since a certain minimum taper is necessary for easy handling.
From European application 230 217 a conical flushing brick without a sheet metal jacket is also known in which the gas supply pipe passes through a base plate of sheet metal and ends directly in the refractory material of the flushing brick. Generally L-shaped gas passages leads radially from the supply pipe, which follow the taper of the flushing brick and end in its front face.
This flushing brick is however extraordinarily expensive in material and construction because of the number of gas-conducting pipes embedded in the refractory material.
Furthermore, particularly in the case of flushing bricks of large section, the high gas pressure on the melt side can also lead to spalling and microcracks parallel to the refractory side. This danger is particularly great in view of the cooling effect of the flushing gas, which can lead to high internal stresses that break off whole pieces from the flushing brick. The associated discontinuous wear quickly leads to failure of the whole flushing brick.